To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, and large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is underway based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
A hybrid automatic repeat request (HARQ) scheme may be used in physical layer transmission between a user equipment (UE) and a base station (eNB). The HARQ scheme attempts to reduce or eliminate transmission errors by repeatedly transmitting data to be transmitted. Repeated transmission of a signal may contribute to suppression of error occurrences and amplification of signal components.
HARQ techniques may be used for many transmission/reception operations in a cellular system. The UE may transmit and receive an original version of data or a redundancy version (RV) thereof to and from the eNB. Whenever data arrives, the receiving side determines success of reception. If data reception is successful, the receiving side transmits a signal indicating no more transmission to the transmitting side. In this case, acknowledgement (ACK) signaling may be used. For example, ACK indicates success of packet reception and NACK indicates failure of packet reception.
The receiving side decodes received data to detect an error and stores the received data in a storage region (e.g., a soft buffer). When no error is detected, the receiving side may transmit ACK feedback to the transmitting side so as not to receive the same data. When an error is detected, the receiving side may transmit NACK feedback to the transmitting side so as to receive another version of the same data within a preset time scheduled next (synchronous/asynchronous for uplink/downlink). The receiving side may decode the newly received version, combine the newly decoded version with the decoded data stored in the soft buffer, and examine the combined data to detect an error. The receiving side may repeat the above procedure. In the current system, several milliseconds are required for the receiving side to complete decoding, error detection, soft buffer writing after reception of data. In addition, a higher layer than the physical layer creates an ACK or NACK packet and transmits the same. The transmitting side may receive this feedback packet and determine whether to perform retransmission.
According to the long term evolution (LTE) standards, the above operations (i.e., reception, decoding, error detection, soft buffer writing, feedback packet generation and transmission, retransmission determination at the transmitter) may take 8 ms (although different from system to system). This applies to both the uplink and the downlink. Hence, it may take 8 ms to receive a piece of data and receive the next piece of data.
As it may take 8 ms to receive a piece of data, this may indicate that the same data may be received again after 8 ms, which is a long time compared to the transmission time interval (TTI). As such, HARQ interleaving is employed to efficiently utilize the time resource, where original pieces of data are transmitted in succession and respective retransmissions are transmitted after 8 ms. For interleaving, up to eight HARQ processes may run in parallel to perform HARQ operation.
FIG. 1 illustrates occurrence of a HARQ process ID collision according to the related art.
Referring to FIG. 1, an HARQ entity functions in communication between the user equipment (UE) and the base station (eNB, evolved Node B). In the UE, the HARQ entity maintains a group of HARQ processes to handle pieces of received data. As the UE performs transmission and reception to and from the eNB, all the HARQ processes are concerned with the eNB. As the eNB performs transmission and reception to and from multiple UEs, the eNB may include multiple HARQ entities, each of which may manage a group of HARQ processes and a soft buffer to handle transmission and reception related to a particular UE.
In device-to-device (D2D) communication, unlike communication between UE and eNB, a UE may communicate with not only an eNB but also another UE. When existing HARQ entity assignment (one HARQ entity and up to eight HARQ processes for one UE, multiple HARQ entities and up to eight HARQ processes for each HARQ entity in one eNB) is used without modifications, eight HARQ processes may be assigned to each UE. In a D2D UE, D2D HARQ processing and WAN HARQ processing may take different delay times. Hence, the number of assigned HARQ processes is to be varied according to the retransmission interval and HARQ processing time. When the number of assigned HARQ processes is less than necessary (i.e., the number of HARQ processes is small in comparison to HARQ processing delay), radio resources may be underutilized, causing inefficiency. When the number of assigned HARQ processes is greater than necessary, memory resources may be unnecessarily wasted. Further, in the case of asynchronous HARQ processing, to notify transmission data using a process identifier, more bits are necessary for ID indication, resulting in waste of system resources.
Referring to FIG. 1, when the HARQ process ID is allocated in sequence from the same HARQ process ID pool, if usage information on HARQ process IDs is not shared between the ID allocation agents (e.g., an eNB and a UE A), a HARQ process ID collision may occur at the common receiving UE (RX UE).
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.